The heart includes a number of pathways that are responsible for the propagation of signals necessary to produce continuous, synchronized contractions. Each contraction cycle begins in the right atrium where a sinoatrial node initiates an electrical impulse. This impulse then spreads across the right atrium to the left atrium, stimulating the atria to contract. The chain reaction continues from the atria to the ventricles by passing through a pathway known as the atrioventricular (AV) node or junction, which acts as an electrical gateway to the ventricles. The AV junction delivers the signal to the ventricles while also slowing it, so the atria can relax before the ventricles contract.
Disturbances in the heart's electrical system may lead to various rhythmic problems that can cause the heart to beat irregularly, too fast or too slow. Irregular heart beats, or arrhythmia, are caused by physiological or pathological disturbances in the discharge of electrical impulses from the sinoatrial node, in the transmission of the signal through the heart tissue, or spontaneous, unexpected electrical signals generated within the heart. One type of arrhythmia is tachycardia, which is an abnormal rapidity of heart action. There are several different forms of atrial tachycardia, including atrial fibrillation and atrial flutter. With atrial fibrillation, instead of a single beat, numerous electrical impulses are generated by depolarizing tissue at one or more locations in the atria (or possibly other locations). These unexpected electrical impulses produce irregular, often rapid heartbeats in the atrial muscles and ventricles. Patients experiencing atrial fibrillation may suffer from fatigue, activity intolerance, dizziness and even strokes.
The precise cause of atrial fibrillation, and in particular the depolarizing tissue causing “extra” electrical signals, is currently unknown. As to the location of the depolarizing tissue, it is generally agreed that the undesired electrical impulses often originate in the left atrial region of the heart. Recent studies have expanded upon this general understanding, suggesting that nearly 90% of these “focal triggers” or electrical impulses are generated in one (or more) of the four pulmonary veins (PV) extending from the left atrium. In this regard, as the heart develops from an embryotic stage, left atrium tissue may grow or extend a short distance into one or more of the PVs. It has been postulated that this tissue may spontaneously depolarize, resulting in an unexpected electrical impulse(s) propagating into the left atrium and along the various electrical pathways of the heart.
A variety of different atrial fibrillation treatment techniques are available, including drugs, surgery, implants, and ablation. While drugs may be the treatment of choice for some patients, drugs typically only mask the symptoms and do not cure the underlying cause. Implantable devices, on the other hand, usually correct an arrhythmia only after it occurs. Surgical and ablation treatments, in contrast, can actually cure the problem by removing and/or ablating the abnormal tissue or accessory pathway responsible for the atrial fibrillation. The ablation treatments rely on the application of various destructive energy sources to the target tissue, including direct current electrical energy, radiofrequency electrical energy, laser energy, microwave energy, ultrasound energy, thermal energy, and the like. The energy source, such as an ablating electrode, is normally disposed along a distal portion of a catheter or instrument. Ablation of the abnormal tissue or accessory pathway responsible for atrial fibrillation has proven highly viable.
Regardless of the application, ablation of tissue is generally achieved by applying the destructive energy source to the target tissue. For some treatments, an ablating element can be formed as a part of a catheter that is delivered via the vascular system to the target site. While relatively non-invasive, catheter-based treatments present certain obstacles to achieving precisely located, complete ablation lesion patterns due to the highly flexible nature of the catheter itself, the confines of the surgical site, etc.
A highly viable alternative device is the hand-held electrosurgical instrument. As used herein, the term “electrosurgical instrument” includes a hand-held instrument capable of ablating tissue or cauterizing tissue, but docs not include a catheter-based device. The instrument is relatively short (as compared to a catheter-based device), and rigidly couples the electrode tip to the instrument's handle that is otherwise held and manipulated by the surgeon. The rigid construction of the electrosurgical instrument requires direct, open access to the targeted tissue. Thus, for treatment of atrial fibrillation via an electrosurgical instrument, it is desirable to gain access to the patient's heart through one or more openings in the patient's chest (such as a sternotomy, a thoracotomy, a small incision and/or a port). In addition, the patient's heart may be opened through one or more incisions, thereby allowing access to the endocardial surface of the heart.
Once the target site (e.g., right atrium, left atrium, epicardial surface, endocardial surface, etc.) is accessible, the surgeon positions the electrode tip of the electrosurgical instrument at the target site. The tip is then energized, ablating (or for some applications, cauterizing) the contacted tissue. A desired lesion pattern is then created (e.g., portions of a known “Maze” procedure) by moving the tip in a desired fashion along the target site. In this regard, the surgeon can easily control positioning and movement of the tip, as the electrosurgical instrument is rigidly constructed and relatively short (in contrast to a catheter-based ablation technique).
Ablation of PV tissue may cause the PV to shrink or constrict due to the relatively small thickness of tissue formed within a PV. Because PVs have a relatively small diameter, a stenosis may result due to the ablation procedure. Even further, other vital bodily structures are directly adjacent each PV. These structures may be undesirably damaged when ablating within a PV. Therefore, a technique has been suggested whereby a continuous ablation lesion pattern is formed in the left atrium wall about the ostium associated with the PV in question. In other words, the PV is electrically isolated from the left atrium by forming an ablation lesion pattern that surrounds the PV ostium. As a result, any undesired electrical impulse generated within the PV would not propagate into the left atrium, thereby eliminating unexpected atria contraction.
Electrosurgical instruments, especially those used for the treatment of atrial fibrillation, have evolved to include additional features that provide improved results for particular procedures. For example, U.S. Pat. No. 5,897,553, the teachings of which are incorporated herein by reference, describes a fluid-assisted electrosurgical instrument that delivers a conductive solution to the target site in conjunction with electrical energy, thereby creating a “virtual” electrode. The virtual electrode technique has proven highly effective in achieving desired ablation while minimizing collateral tissue damage. Other electrosurgical instrument advancements have likewise optimized system performance. However, a common characteristic associated with available electrosurgical instruments is a “designed-in” directional orientation. That is to say, electrosurgical devices, and especially those used for atrial fibrillation treatment procedures, are curved along a length thereof, as exemplified by the electrosurgical instrument of U.S. Pat. No. 5,897,553. In theory, this permanent curved feature facilitates the particular procedure (or lesion pattern) for which the electrosurgical instrument is intended. Unfortunately, however, the actual lesion pattern formation technique and/or bodily structure may vary from what is expected, so that the curve is less than optimal. Additionally, the pre-made curve may be well suited for one portion of a particular procedure (e.g., right atrium ablation pattern during the Maze procedure), but entirely inapplicable to another portion (e.g., left atrium ablation during the Maze procedure). As a result, the electrosurgical instrument design may actually impede convenient use by a surgeon.
Electrosurgical instruments continue to be highly useful for performing a variety of surgical procedures, including surgical treatment of atrial fibrillation. While certain advancements have improved overall performance, the accepted practice of imparting a permanent curve or other shape variation into the instrument itself may impede optimal usage during a particular procedure. Therefore, a need exists for an electrosurgical instrument that, as initially presented to a surgeon, is indifferent to rotational orientation, and further is capable of independently maintaining a number of different shapes as desired by the surgeon.
In cases of atrial fibrillation, it is desirable to identify the origination point of the undesired electrical impulses prior to ablation. Mapping may be accomplished by placing one or more mapping electrodes into contact with the tissue in question. Mapping of tissue may occur by placing one or more mapping electrodes into contact with the endocardial surface of the heart and/or the epicardial surface of the heart. Therefore, a need exists for a mapping instrument that is capable of mapping the heart, e.g., during an ablation procedure. Preferably, this mapping instrument, as initially presented to a surgeon, would be indifferent to rotational orientation, and further would be capable of independently maintaining a number of different shapes as desired by the surgeon.
As used herein, the term “mapping instrument” includes a hand-held instrument capable of pacing and/or mapping cardiac tissue. The mapping instrument is similar to the electrosurgical instrument described above in that it is relatively short (as compared to a catheter-based device), and rigidly couples an electrode tip to the instrument's handle that is otherwise held and manipulated by the surgeon. The rigid construction of the mapping instrument requires direct, open access to the targeted tissue. Thus, for mapping and/or pacing of cardiac tissue via the mapping instrument, it is desirable to gain access to the patient's heart through one or more openings in the patient's chest (such as a sternotomy, a thoracotomy, a small incision and/or a port). In addition, the patient's heart may be opened through one or more incisions, thereby allowing access to the endocardial surface of the heart.
Once the target site (e.g., right atrium, left atrium, right ventricle, left ventricle, epicardial surface, endocardial surface, pulmonary veins, etc.) is accessible, the surgeon positions the electrode tip of the mapping instrument at the target site. The surgeon can easily control positioning and movement of the tip, as the mapping instrument is rigidly constructed and relatively short (in contrast to a catheter-based technique).
In cardiac resynchronization therapy (CRT) for the treatment of patients with congestive heart failure and ventricular dysynchrony, the heart is paced from both ventricles simultaneously by placing two ventricular leads on opposite sides of the heart. Various studies have shown that lead location: can affect cardiac function; therefore, optimizing placement of the left ventricular lead on the left ventricular free wall may improve CRT results and patient outcomes.
Venous anatomy may not allow a transveous lead to be placed in an optimal location. However, an epicardial lead may be placed at any site on the heart, creating the opportunity to optimize lead position. There are several situations during implantation of a left ventricular lead in which one should consider converting from a transveous lead procedure to an epicardial lead procedure. These include inability to cannulate the coronary sinus or the desired coronary vein, inability of the lead to properly lodge in the vein or lack of any vein in the preferred location.
Interest in optimizing left ventricular lead placement for cardiac resynchronization therapy is being supported by growing data that demonstrate the location of the lead on the heart can affect hemodynamics and improve patient outcomes. Epicardial mapping is a technique to determine a patient-specific location for the left-sided pacing lead in CRT procedures.